Seasonal characteristics of nitric oxide emission from a typical Chinese rice-wheat rotation during the non-waterlogged period

Nitric oxide emissions from a typical rice-wheat rotation system in southeastern China were continuously measured with an automatic system in 1996-1997. The seasonal pattern of the NO emissions was characterized for the non-waterlogged period of a rotation cycle. Nitric oxide emissions during the period from March through June were 3.9-6.3 folds for the fertilized plots and 1.6 folds for the unfertilized plot larger than those from November through December. Nitric oxide emissions were not detectable during the winter period from January through February. Amendment of synthetic fertilizer N significantly enhanced the NO emission by a factor of 6.5, but the enhancement was significantly mitigated by 25% through substituting ca. 16% of the synthetic fertilizer N with organic N from fermented crop residues or by 21% through deep tillage. The NO-N emission factor, defined as the amount of NO-N released per unit of synthetic fertilizer N input, was determined to be 0.025 kg NO-N kg (-1) of N applied for the non-waterlogged period, which was reduced by 32% through substituting part of the synthetic N fertilizer with fermented crop residues or by 24% through deep tillage. In addition, the NO emission factor, defined as the amount of NO-N emitted from unit unfertilized area per day, was observed to be ca. 3.8 g N ha (-1) d (-1) . Approximately 0.55 Tg N yr (-1) was likely released as NO from Chinese cultivated lands.